1. Field of the Invention
The present invention relates generally to the preparation of sulfurized alkylphenols, and, more particularly, preparation thereof via reaction of an alkylphenol with sulfur in the presence of a catalyst mixture comprising water, a dihydric alcohol and an alkaline earth metal oxide or hydroxide. The sulfurized alkylphenols prepared according to the present invention are useful in the lubricant art as oxidation inhibitors and as intermediates in the preparation of neutral and overbased phenate detergents.
2. Discussion of Prior Art
The preparation of sulfurized alkylphenols using sulfur halides as sulfurization agents is well known in the art and is described, e.g., in U.S. Pat. No. 4,104,180. Sulfur halides, however, are relatively expensive reagents and in addition, products thus obtained contain rather corrosive halide components unless the products are subjected to complicated purification steps.
Elemental sulfur is preferred as a sulfurization reagent for alkylphenols. However, elemental sulfur is not as reactive as sulfur halides and a catalyst or catalyst mixture is therefore required. U.S. Pat. No. 3,509,053 disclosed the use of a sodium hydroxide catalyst. However, the presence of sodium in the product or lubricant additives prepared from this product has the disadvantage that the sodium can contribute to alkaline cracking of engine valves particularly in railroad applications. U.S. Pat. No. 3,912,707 described the use of an alkaline earth metal base and dihydric alcohol mixture to promote alkylphenol sulfurization as the first step of a two-step process for phenates. The presence of dihydric alcohol in the finished products, however, contributes to engine lacquer deposits.